Radiotherapy is a form of cancer treatment that uses mega voltage x-rays from a linear accelerator to kill the tumor. Current clinical practice is to deliver the dose of radiation over a number of weeks that includes safety margins, where the dose is a compromise to between tumor kill and normal tissue toxicity. Here, no change is made to account for the individual patient during treatment, such as the response or motion of tumor etc.
An MRI-Linac is a new state-of-the art radiotherapy treatment system that combines a linear accelerator with a magnetic resonance imaging (MRI) scanner. This enables high quality images of the anatomy to be used to guide treatment in real-time offering the ability to treat tumous with greater dose and higher precision, thus improving outcomes in patients that are known to be poorly treated. Several versions of MRI-Linac are being actively pursued, marking a sea change in radiation treatment.
In vivo dosimetry is widely recognized as an effective procedure to mitigate errors in radiation therapy and is recommended for treatments involving new equipment or one-off special cases. Current methods of in vivo dosimetry are limited and cannot be used in real-time and/or in magnetic fields. Overcoming this is of vital importance in maintaining acceptable safety levels for complex and individualized treatments on an MRI-Linac.
What is needed is a method of monitoring a state of a Linac beam in an MRI-Linac system for real-time in vivo patient dosimetry in the presence of the MRI magnetic field.